1. Field of the Invention
This invention relates to advanced military grade communications jamming systems and, more specifically, to a Method and Apparatus for Surgical High Speed Follower Jamming Based on Selectable Target Direction.
2. Description of Related Art
Modern military grade communication systems today employ short, burst type transmissions that constantly cycle through a secret sequence of frequencies in order to prevent detection and jamming. Such systems are commonly known as frequency hoppers. Typically, these systems (both foreign and domestic) only transmit on a particular frequency for no more than a few milliseconds at the most. This creates a problem for those who want to detect and jam such transmissions as they happen so quickly.
The continuing development of modern military frequency-hopping systems magnifies the complexities of electronic warfare. Today's frequency-hopping technology is advancing quickly, allowing frequency-hopping communication nets to use many frequencies (hop sets), much faster than ever before (hop speeds). A fundamental change in RF detection and jamming efficiency is needed for the modern military force to achieve and maintain electronic warfare dominance in the theater of war. The modern military force needs the capability to detect and combat any and all enemy communications in a specified sector of the battlefield, no matter how fast they hop frequencies to attempt to avoid detection.
Practically, it is not feasible to simply “splash” the radio frequency spectrum with random noise in order to jam such transmissions. The reasons are that it requires an unpractical amount of power to apply sufficient RF energy to wash out all transmissions. In addition, there may be friendly transmissions that should not be jammed. Also, since the duration of the target transmissions is so short, it is not practical to have (for instance) a CPU that is programmed to evaluate signals, make a determination, and then command transmitters to jam. There is simply not enough time to engage the frequency hopping signals before they have moved on to a new frequency.
Jamming systems attempt to solve the short cycle problem in one of three ways:    1. Barrage jamming: This type of jamming involves “splashing” a segment of the radio frequency (RF) spectrum with random or distributed noise in order to jam frequency-hopping transmissions by brute force. Barrage jamming is impractical for several reasons, including the amount of power needed to apply sufficient RF energy to wash out all transmissions. This is extremely inefficient, since jamming energy is often applied to areas of the RF spectrum where there is no enemy communications traffic, thus the energy is wasted. Also, fratricide of friendly transmissions that are near to the enemy communications is another problem of barrage jamming.    2. Follower jamming: this type of jamming, also called “fast-reaction” jamming, requires the reception of signals and the automatic selective jamming of those signals soon thereafter for as long as the enemy transmission is active. Follower jamming also has the drawback that any and all signals detected within its dynamic range will be jammed, regardless of whether it is emanating from a friend or from an enemy. The follower jammer keys off of the simple presence of signal energy at a particular frequency; there is no discrimination between friend and enemy. Thus, there are fratricide issues and inefficiency issues with wasting jammer signal energy on friendly communications.    3. Surgical follower jamming: Surgical follower jamming that is afforded by this invention is the only practical jamming method known to date for effectively jamming enemy fast frequency-hopping transmissions and preventing fratricide. Prior to the present invention, however, no follower jammer was responsive and/or had surgical accuracy adequate to truly defeat frequency-hopping transmitters.
The prior-art of FIG. 1 shows the effect of a present-day barrage jamming system. It is a drawing of several plots of RF power at a certain frequency range. Each plot depicts the same power and frequency ranges, but at different instants in time. The time order of the plots is as follows: 1, 1+x, 2, 2+x, 3, 3+x; x being the reaction time of the barrage jammer (assumed to be much smaller than one time unit). Thus the top row of plots shows the spectrum while the jammer is in the “look-through” state, while the bottom row shows the spectrum while the jammer is in the matching “attack” state.
As depicted in the upper set of graphs, an enemy signal transmission is detected at a frequency very close to a friend. As T=1 moves to T=2 and T=3, the enemy transmission frequency is “hopping” to the left and right (up and down in frequency) as compared to the friendly transmitter.
The lower set of graphs depicts the operation of a Barrage jammer. Barrage jammers essentially choose a band or segment of frequency on which to transmit the jamming signal. During the barrage jammer's attack phase, a segment of the RF spectrum is “splashed” with noise in an attempt to disrupt enemy transmissions in that segment of the spectrum. Periodically, the jammer stops jamming to see if any signals are still present in the frequency segment being focused upon. Such an operation is called a “look-through” and is necessary in case the target transmissions have moved to a new segment of the spectrum.
Such a traditional setup is suitable for the jamming of relatively long duration communication signals such as voice or a low speed data links. But this simple system has several drawbacks including the fact that a massive amount of RF power is necessary to splash any sufficiently wide segment of the RF spectrum. As the figure shows, an overwhelming percentage of this power is wasted. Another drawback is that any friendly transmissions in the segment of focus will also be jammed. A third drawback is that the power of the jamming signals is usually lower than the target signal, so that the target signal may not actually be disrupted at all.
The prior-art of FIG. 2 shows the effect of a present-day follower jamming system. This system solves the power issues of the barrage jamming system, but it has its own drawbacks. The main drawback of the follower jamming system is the fratricide problem pictured here. Since the follower jammer does not discriminate between friendly and enemy transmissions in a particular frequency segment, it will transmit jamming signals on any frequency in the segment of interest where a transmission is detected, whether friend or enemy. As a result, while the follower jammer is jamming enemy communications, friendly communications are also jammed, just like the barrage jamming system.
What is needed therefore in order to feasibly detect and jam modern fast-hopping transmissions as efficiently as possible is a System that has not only has: 1) The near-real time ability to jam detected signals, but also 2) The ability to identify the specific compass direction, or sector, of the source of the frequency-hopping transmissions, also in near real time. The user of such a system could then surgically jam enemy transmissions simply by specifying the compass sector of the enemy transmission source to be jammed. The direction of the enemy transmitters is usually known; many current and possible theaters of war are in littoral (coastal) terrain, where the direction of enemy transmitters is trivially known.